The present invention relates to a label suitable for in-mold forming and a method for fabricating thereof.
The in-mold forming method is known as a method for fabricating, by integral molding, a synthetic resin formed product intrinsically bearing a label. In this method, a label is first placed on the inner wall of the metal mold, and then a source resin such as polyethylene and polypropylene is directly fed into the metal mold to obtain a formed product by injection molding, hollow molding or in-mold bead foaming. Also in the process of using a polypropylene or polyethylene sheet, a label can be attached based on the same principle by a method utilizing differential pressure generated under heating of the sheet (vacuum molding, differential pressure molding).
A variety of labels have been proposed for use in such in-mold forming. An exemplary label is that obtained by coating on a base layer a solution of low-melting-point olefin resins such as ethylene-vinyl acetate copolymer using a gravure coater or the like and by successive drying; where the base layer comprises a non-stretched extruded film made of crystalline polypropylene or high-density polyethylene compounded with inorganic fine powder, or an inflation-molded film. There are also proposed films such that fabricated by stacking a low-melting-point olefinic resin film on one surface of the base layer, using an adhesive or by direct extrusion lamination.
This fabricated label, however, is disadvantageous in that the film may easily be stretched due to tensile force when it is subjected to gravure printing in a wound-up state, which may result in misalignment of patterns and prevent high-definition printing. Still another problem is that crimping of the film due to lack of its stiffness, which is likely to occur when the label cut into a predetermined size is placed on the inner wall of the metal mold using a robot inserter, so that high-speed placement of the film will be unsuccessful. Moreover, a label coated or laminated with an adhesive layer requires excessive process steps and, as a result, higher production cost.
On the other hand, as a label for overcoming the foregoing drawbacks, proposed is a label which is fabricated by laminating a low-melting-point olefinic resin such as low-density polyethylene or ethylene-vinyl acetate copolymer on a base layer comprising a sheet of longitudinally stretched crystalline polypropylene compounded with inorganic fine powder, and by transversely stretching the laminate using a tenter oven. Such label, however, contains relatively large disc-shaped voids generated in the base layer by the biaxial stretching, and the voids will be transformed in the thickness direction to exhibit so-called xe2x80x9corange peel texturexe2x80x9d when in-mold formed container causes mold shrinkage together with the label attached thereon. Moreover, since the label having a biaxially stretched base layer has a high stiffness both in longitudinal and transverse directions, the container attached with such label may distort during the mold shrinkage due to a limited deformability of the label.
For addressing the above problems in the prior art, it is therefore an object of the present invention to provide a label suitable for in-mold forming. That is, the present invention provides a label excellent in smoothness of the adhesive layer, Clark stiffness and adhesiveness, and less causative of blisters or orange peel texture after in-mold forming, and of deformation of the containers. It is another object of the present invention to provide a simple and low-cost method for fabricating such a label.